Renewable resources are intermittent for producing needed replacement energy in various forms such as electricity, hydrogen, fuel alcohols, and methane. Solar energy is a daytime event, and the daytime concentration varies seasonally and with weather conditions. In most areas, wind energy is intermittent and highly variable in magnitude. Falling water resources vary seasonally and are subject to extended draughts. In most of the earth's landmass, biomass is seasonally variant and subject to draughts. Throughout the world, considerable energy that could be delivered by hydroelectric plants, wind farms, biomass conversion, and solar collectors is wasted because of the lack of practical ways to save kinetic energy, fuel, and/or electricity until it is needed.
The world population and demand for energy has grown to the point of requiring more oil than can be produced. Future rates of production will decline while demands of increasing population and increasing dependence upon energy-intensive goods and services accelerate. This will continue to hasten the rate of fossil depletion. Cities suffer from smog caused by the use of fossil fuels. Utilization of natural gas including natural gas liquids such as ethane, propane, and butane for non-fuel purposes has increased exponentially in applications such as packaging, fabrics, carpeting, paint, and appliances that are made largely from thermoplastic and thermoset polymers.
Coal has relatively low hydrogen to carbon ratio. Oil has higher hydrogen to carbon ratio and natural gas has the highest hydrogen to carbon ratio of fossil hydrocarbons. Using oil as the representative medium, the global burn rate of fossil hydrocarbons now exceeds the equivalent of 200 million barrels of oil per day.
Global oil production has steadily increased to meet growing demand but the rate of oil discovery has failed to keep up with production. Peak production of oil has occurred and the rates of oil production in almost all known reserves are steadily decreasing. After peak production, the global economy experiences inflation of every energy-intensive and petrochemical-based product. Conflict over remaining fossil fuel resources and the utilization of oil to fuel and lubricate machines of destruction spurred World War I, World War II, and every war since then. Replacing the fossil fuel equivalent of 200 million barrels of oil each day requires development of virtually every practical approach to renewable energy production, distribution, storage, and utilization.
Air and water pollution caused by fossil fuel production and combustion now degrade every metropolitan area along with fisheries, farms, and forests. Mercury and other heavy metal poisoning of fisheries and farm soils are increasingly traced to coal combustion. Global climate changes including more powerful hurricanes and tornadoes, torrential rainstorms, and increased incidents of fire losses due to lightning strikes in forests and metropolitan areas are closely correlated to atmospheric buildup of greenhouse gases released by combustion of fossil fuels. With increased greenhouse gas collection of solar energy in the atmosphere, greater work is done by the global atmospheric engine including more evaporation of ocean waters, melting of glaciers and polar ice caps, and subsequent extreme weather events that cause great losses of improved properties and natural resources.
Previous attempts to utilize multifuel selections including hydrogen, producer gas, and higher hydrogen-to-carbon ratio fuels such as methane, fuel alcohols, and various other alternative fuels along with or in place of gasoline and diesel fuels have variously encountered and failed to solve difficult problems, and these attempts are expensive, produce unreliable results, and frequently cause engine degradation or damage including:
(1) Greater curb weight to increase engine compression ratio and corresponding requirements for more expensive, stronger, and heavier pistons, connecting rods, crankshafts, bearings, flywheels, engine blocks, and support structure for acceptable power production and therefore heavier suspension springs, shock absorbers, starters, batteries, etc.
(2) Requirements for more expensive valves, hardened valve seats, and machine shop installation to prevent valve wear and seat recession.
(3) Requirements to supercharge to recover power losses and drivability due to reduced fuel energy per volume and to overcome compromised volumetric and thermal efficiencies.
(4) Multistage gaseous fuel pressure regulation with extremely fine filtration and very little tolerance for fuel quality variations including vapor pressure and octane and cetane ratings.
(5) Engine coolant heat exchangers for prevention of gaseous fuel pressure regulator freeze-ups.
(6) Expensive and bulky solenoid operated tank shutoff valve (TSOV) and pressure relief valve (PRD) systems.
(7) Remarkably larger flow metering systems.
(8) After dribble delivery of fuel at wasteful times and at times that produce back-torque.
(9) After dribble delivery of fuel at harmful times such as the exhaust stroke to reduce fuel economy and cause engine or exhaust system damage.
(10) Engine degradation or failure due to pre-detonation and combustion knock.
(11) Engine hesitation or damage due to failures to closely control fuel viscosity, vapor pressure, octane or cetane rating, and burn velocity,
(12) Engine degradation or failure due to fuel washing, vaporization and burn-off of lubricative films on cylinder walls and ring or rotor seals.
(13) Failure to prevent formation of oxides of nitrogen during combustion.
(14) Failure to prevent formation of particulates due to incomplete combustion.
(15) Failure to prevent pollution due to aerosol formation of lubricants in upper cylinder areas.
(16) Failure to prevent overheating of pistons, cylinder walls, and valves consequent friction increases, and degradation.
(17) Failure to overcome damaging backfiring in intake manifold and air cleaner components.
(18) Failure to overcome damaging combustion and/or explosions in the exhaust system.
(19) Failure to overcome overheating of exhaust system components.
(20) Failure to overcome fuel vapor lock and resulting engine hesitation or failure.
Further, special fuel storage tanks are required for low energy density fuels. Storage tanks designed for gasoline, propane, natural gas, and hydrogen are discrete to meet the widely varying chemical and physical properties of each fuel. A separate fuel tank is required for each fuel type that a vehicle may utilize. This dedicated tank approach for each fuel selection takes up considerable space, adds weight, requires additional spring and shock absorber capacity, changes the center of gravity and center of thrust, and is very expensive.
In conventional approaches, metering alternative fuel choices such as gasoline, methanol, ethanol, propane, ethane, butane hydrogen, or methane into an engine may be accomplished by one or more gaseous carburetors, throttle body fuel injectors, or timed port fuel injectors. Power loss sustained by each conventional approach varies because of the large percentage of intake air volume that the expanding gaseous fuel molecules occupy. Thus, with reduced intake air entry, less fuel can be burned, and less power is developed.
At standard temperature and pressure (STP) gaseous hydrogen occupies 2,800 times as much volume as liquid gasoline for delivery of equal combustion energy. Gaseous methane requires about 900 times as much volume as liquid gasoline to deliver equal combustion energy.
Arranging for such large volumes of gaseous hydrogen or methane to flow through the vacuum of the intake manifold, through the intake valve(s), and into the vacuum of a cylinder on the intake cycle and to do so along with enough air to support complete combustion to release the heat needed to match gasoline performance is a monumental challenge that has not been adequately met. Some degree of power restoration may be available by resorting to larger displacement engines. Another approach requires expensive, heavier, more complicated, and less reliable components for much higher compression ratios and/or supercharging the intake system. However, these approaches cause shortened engine life and much higher original and/or maintenance costs unless the basic engine design provides adequate structural sections for stiffness and strength.
Engines designed for gasoline operation are notoriously inefficient. To a large extent this is because gasoline is mixed with air to form a homogeneous mixture that enters the combustion chamber during the throttled conditions of the intake cycle. This homogeneous charge is then compressed to near top dead center (TDC) conditions and spark ignited. Homogeneous charge combustion causes immediate heat transfer from 4,500° F. to 5,500° F. (2,482° C. to 3,037° C.) combustion gases to the cylinder head, cylinder walls, and piston or corresponding components of rotary engines. Protective films of lubricant are burned or evaporated, causing pollutive emissions, and the cylinder and piston rings suffer wear due to lack of lubrication. Homogeneous charge combustion also forces energy loss as heat is transferred to cooler combustion chamber surfaces, which are maintained at relatively low temperatures of 160° F. to 240° F. (71° C. to 115° C.) by liquid and/or air-cooling systems.
Utilization of hydrogen or methane as homogeneous charge fuels in place of gasoline presents an expensive challenge to provide sufficient fuel storage to accommodate the substantial energy waste that is typical of gasoline engines. Substitution of such cleaner burning and potentially more plentiful gaseous fuels in place of diesel fuel is even more difficult. Diesel fuel has a greater energy value per volume than gasoline. Additional difficulties arise because gaseous fuels such as hydrogen, producer gas, methane, propane, butane, and fuel alcohols such as ethanol or methanol lack the proper cetane ratings and do not ignite in rapidly compressed air as required for efficient diesel-engine operation. Diesel fuel injectors are designed to operate with a protective film of lubrication that is provided by the diesel oil. Further, diesel fuel injectors only cyclically pass a relatively minuscule volume of fuel, which is about 3,000 times smaller (at STP) than the volume of hydrogen required to deliver equivalent heating value.
Most modern engines are designed for minimum curb weight and operation at substantially excess oxygen equivalence ratios in efforts with homogeneous charge mixtures of air and fuel to reduce the formation of oxides of nitrogen by limiting the peak combustion temperature. In order to achieve minimum curb weight, smaller cylinders and higher piston speeds are utilized. Higher engine speeds are reduced to required shaft speeds for propulsion through higher-ratio transmission and/or differential gearing.
Operation at excess oxygen equivalence ratios requires greater air entry, and combustion chamber heads often have two or three intake valves and two or three exhaust valves. This leaves very little room in the head area for a direct cylinder fuel injector or a spark plug. Operation of higher speed valves by overhead camshafts further complicates and reduces the space available for direct cylinder fuel injectors and spark plugs. Designers have used virtually all of the space available over the pistons for valves and valve operators and have barely left room to squeeze in spark plugs for gasoline ignition or diesel injectors for compression-ignition engines.
Therefore, it is extremely difficult to deliver by any conduit greater in cross-section than the gasoline engine spark plug or the diesel engine fuel injector equal energy by alternative fuels such as hydrogen, methane, propane, butane, ethanol, or methanol, all of which have lower heating values per volume than gasoline or diesel fuel. The problem of minimal available area for spark plugs or diesel fuel injectors is exacerbated by larger heat loads in the head due to the greater heat gain from the three to six valves that transfer heat from the combustion chamber to the head and related components. Further exacerbation of the space and heat load problems is due to greater heat generation in the cramped head region by cam friction, valve springs, and valve lifters in high-speed operations.
In many ways, piston engines have been the change agents and have provided essential energy conversion throughout the industrial revolution. Today compression ignition internal combustion piston engines using cetane-rated diesel fuel power most of the equipment for farming, mining, rail and marine heavy hauling, and stationary power systems, along with new efforts in smaller engines with higher piston speeds to improve fuel efficiency of passenger and light truck vehicles. Lower compression internal combustion piston engines with spark ignition are less expensive to manufacture and utilize octane-rated fuels to power a larger portion of the growing population of 900 million passenger and light truck vehicles.
Octane and cetane-rated hydrocarbon fuel applications in conventional internal combustion engines produce unacceptable levels of pollutive emissions such as unburned hydrocarbons, particulates, oxides of nitrogen, carbon monoxide, and carbon dioxide.
Conventional spark ignition consists of a high voltage but low energy ionization of a mixture of air and fuel. Conventional spark energy magnitudes of about 0.05 to 0.15 joule are typical for normally aspirated engines equipped with spark plugs that operate with compression ratios of 12:1 or less. Adequate voltage to produce such ionization must be increased with higher ambient pressure in the spark gap. Factors requiring higher voltage include leaner air-fuel ratios and a wider spark gap as may be necessary for ignition, increases in the effective compression ratio, supercharging, and reduction of the amount of impedance to air entry into a combustion chamber. Conventional spark ignition systems fail to provide adequate voltage generation to dependably provide spark ignition in engines such as diesel engines with compression ratios of 16:1 to 22:1 and often fail to provide adequate voltage for unthrottled engines that are supercharged for purposes of increased power production and improved fuel economy.
Failure to provide adequate voltage at the spark gap is most often due to inadequate dielectric strength of ignition system components such as the spark plug porcelain and spark plug cables.
High voltage applied to a conventional spark plug, which essentially is at the wall of the combustion chamber, causes heat loss of combusting homogeneous air-fuel mixtures that are at and near all surfaces of the combustion chamber including the piston, cylinder wall, cylinder head, and valves. Such heat loss reduces the efficiency of the engine and may degrade the combustion chamber components that are susceptible to oxidation, corrosion, thermal fatigue, increased friction due to thermal expansion, distortion, warpage, and wear due to loss of viability of overheated or oxidized lubricating films.
Even if a spark at the surface of the combustion chamber causes a sustained combustion of the homogeneous air-fuel mixture, the rate of flame travel sets the limit for completion of combustion. The greater the amount of heat that is lost to the combustion chamber surfaces, the greater the degree of failure to complete the combustion process. This undesirable situation is coupled with the problem of increased concentrations of unburned fuel such as hydrocarbons vapors, hydrocarbon particulates, and carbon monoxide in the exhaust.
Efforts to control air-fuel ratios and provide leaner burn conditions for higher fuel efficiency and to reduce peak combustion temperature and hopefully reduce production of oxides of nitrogen cause numerous additional problems. For example, leaner air-fuel ratios burn slower than stoichiometric or fuel-rich mixtures. Moreover, slower combustion requires greater time to complete the two- or four-stroke operation of an engine, thus reducing the specific power potential of the engine design. With adoption of natural gas as a replacement for gasoline or diesel fuel must come recognition of the fact that natural gas combusts much slower than gasoline and that natural gas will not facilitate compression ignition if it is substituted for diesel fuel.
In addition, modern engines provide far too little space for accessing the combustion chamber with previous electrical insulation components having sufficient dielectric strength and durability for protecting components that must withstand cyclic applications of high voltage, corona discharges, and superimposed degradation due to shock, vibration, and rapid thermal cycling to high and low temperatures. Furthermore, previous approaches to homogeneous and stratified charge combustion fail to overcome limitations related to octane or cetane dependence and fail to provide control of fuel dribbling at harmful times or adequate combustion speed to enable higher thermal efficiencies, and they fail to prevent combustion-sourced oxides of nitrogen.
In order to meet desires for multifuel utilization along with lower curb weight and greater air entry it is ultimately important to allow unthrottled air entry into the combustion chambers, to directly inject gaseous, cleaner-burning, and less-expensive fuels, and to provide stratified-charge combustion as a substitute for gasoline and diesel (petrol) fuels. However, this desire encounters the extremely difficult problems of providing dependable metering of such widely variant fuel densities, vapor pressures, and viscosities to then assure subsequent precision timing of ignition and completion of combustion events. In order to achieve positive ignition, it is necessary to provide a spark-ignitable air-fuel mixture in the relatively small gap between spark electrodes.
If fuel is delivered by a separate fuel injector to each combustion chamber in an effort to produce a stratified charge, elaborate provisions such as momentum swirling, ricocheting, or rebounding the fuel from combustion chamber surfaces into the spark gap must be arranged, but these approaches always cause compromising heat losses to combustion chamber surfaces as the stratified charge concept is sacrificed. If fuel is controlled by a metering valve at some distance from the combustion chamber, “after dribble” of fuel at wasteful or damaging times, including times that produce torque opposing the intended output torque, will occur. Either approach inevitably causes much of the fuel to “wash” or impinge upon cooled cylinder walls in order for some small amount of fuel to be delivered in a spark-ignitable air-fuel mixture in the spark gap at the precise time of desired ignition. This results in heat losses, loss of cylinder-wall lubrication, friction-producing heat deformation of cylinders and pistons, and loss of thermal efficiency due to heat losses from work production by expanding gases to non-expansive components of the engine.
Efforts to produce swirl of air entering the combustion chamber and to place lower density fuel within the swirling air suffer two harmful characteristics. The inducement of swirl causes impedance to the flow of air into the combustion chamber and thus reduces the amount of air that enters the combustion chamber to cause reduced volumetric efficiency. After ignition, products of combustion are rapidly carried by the swirl momentum to the combustion chamber surfaces and adverse heat loss is accelerated.
Past attempts to provide internal combustion engines with multifuel capabilities, such as the ability to change between fuel selections such as gasoline, natural gas, propane, fuel alcohols, producer gas and hydrogen, have proven to be extremely complicated and highly compromising. Past approaches induced the compromise of detuning all fuels and canceling optimization techniques for specific fuel characteristics. Such attempts have proven to be prone to malfunction and require very expensive components and controls. These difficulties are exacerbated by the vastly differing specific energy values of such fuels, wide range of vapor pressures and viscosities, and other physical property differences between gaseous fuels and liquid fuels. Further, instantaneous redevelopment of ignition timing is required because methane is the slowest burning of the fuels cited, while hydrogen burns about 7 to 10 times faster than any of the other desired fuel selections.
Additional problems are encountered between cryogenic liquid or slush and compressed-gas fuel storage of the same fuel substance. Illustratively, liquid hydrogen is stored at −420° F. (−252° C.) at atmospheric pressure and causes unprotected delivery lines, pressure regulators, and injectors to condense and freeze atmospheric water vapor and to become ice damaged as a result of exposure to atmospheric humidity. Cryogenic methane encounters similar problems of ice formation and damage. Similarly, these super cold fluids also cause ordinary metering orifices, particularly small orifices, to malfunction and clog.
The very difficult problem that remains and must be solved is how can a vehicle be refueled quickly with dense liquid fuel at a cryogenic (hydrogen or methane) or ambient temperature (propane or butane), and at idle or low power levels use vapors of such fuels, and at high power levels use liquid delivery of such fuels in order to meet energy production requirements?
At atmospheric pressure, injection of cryogenic liquid hydrogen or methane requires precise metering of a very small volume of dense liquid compared to a very large volume delivery of gaseous hydrogen or methane. Further, it is imperative to precisely produce, ignite, and combust stratified charge mixtures of fuel and air regardless of the particular multifuel selection that is delivered to the combustion chamber.
Accomplishment of essential goals including highest thermal efficiency, highest mechanical efficiency, highest volumetric efficiency, and longest engine life with each fuel selection requires precise control of the fuel delivery timing, combustion chamber penetration, and pattern of distribution by the entering fuel, and precision ignition timing, for optimizing air utilization, and maintenance of surplus air to insulate the combustion process with work-producing expansive medium.
In order to sustainably meet the energy demands of the global economy, it is necessary to improve production, transportation, and storage of methane and hydrogen by virtually every known means. A gallon of cryogenic liquid methane at −256° C. provides an energy density of 89,000 BTU/gal, about 28% less than a gallon of gasoline. Liquid hydrogen at −252° C. provides only about 29,700 BTU/gal, or 76% less than gasoline.
It has long been desired to interchangeably use methane, hydrogen or mixtures of methane and hydrogen as cryogenic liquids or compressed gases in place of gasoline in spark-ignited engines. But this goal has not been satisfactorily achieved, and as a result, the vast majority of motor vehicles remain dedicated to petrol even though the costs of methane and many forms of renewable hydrogen are far less than gasoline. Similarly it has long been a goal to interchangeably use methane, hydrogen or mixtures of methane and hydrogen as cryogenic liquids and/or compressed gases in place of diesel fuel in compression-ignited engines but this goal has proven even more elusive, and most diesel engines remain dedicated to pollutive and more expensive diesel fuel.